Fix input character passing

escape_default is actually not the right function here, because it is
meant for escaping strings with C-like rules.

For example, character " becomes the string \"

Since Strings are UTF-8, we can just directly allocate a String as an
intermediate buffer.

src/lib.rs

@@ -231,17 +231,14 @@ impl ImGui {
         io.key_map[key as usize] = mapping as i32;
     }
     pub fn add_input_character(&mut self, character: char) {
-        if !character.is_control() {
-            // TODO: This is slightly better. We should use char::encode_utf8 when it stabilizes
-            // to allow us to skip the string intermediate since we can then go directly
-            // to bytes
-            let utf8_str: String = character.escape_default().collect();
-            let mut bytes = utf8_str.into_bytes();
-            // into_bytes does not produce a c-string, we must append the null terminator
-            bytes.push(0);
-            unsafe {
-                imgui_sys::ImGuiIO_AddInputCharactersUTF8(bytes.as_ptr()  as *const i8);
-            }
+        // TODO: This is slightly better. We should use char::encode_utf8 when it stabilizes
+        // to allow us to skip the string intermediate since we can then go directly
+        // to bytes
+        let mut string = String::new();
+        string.push(character);
+        string.push('\0');
+        unsafe {
+            imgui_sys::ImGuiIO_AddInputCharactersUTF8(string.as_ptr() as *const i8);
         }
     }
     pub fn get_time(&self) -> f32 { unsafe { imgui_sys::igGetTime() } }